For many reasons, leptospirosis is a disease that companion animal clinicians should have under consideration at almost all times.

It’s an Emerging Disease

The incidence of cases in the United States has been increasing for many years.1,2Additionally, there are reports of outbreaks in geographies, such as Arizona in 2017, that had historically been considered low risk due to their climate.3

Clinical Presentations Vary

Cases of acute leptospirosis are often thought of as presenting with acute renal failure or hepatic disease.4However, it is beyond important to be fully aware that infection can affect different body systems, which can lead to a wide variety of clinical signs—hence its nickname “the great pretender.”Disease severity can also vary.4,5Both experimental infection and serologic surveys have demonstrated that infection can be subclinical, and studies of naturally infected dogs have reported that they frequently present with only mild signs such as lethargy, vomiting, anorexia, and polydipsia.4,5Icterus and fever may not be as common at presentation as once thought.5

It Is Zoonotic

In fact, it is often referred to as the most common and widespread zoonotic disease in the world.6The CDC reports that in the United States cases of human leptospirosis are also on the rise and many urban cases may be related to exposure to dog or rat urine.Lepto has been reported in more than 150 mammalian species.Although pet dogs are rarely reported as an exposure source for human leptospirosis, transmission is possible and another reason why discussion of both risks and prevention should occur in the veterinary hospital setting.4

Diagnosis Requires Testing

In order to definitively diagnose cases diagnostic testing is necessary, or to put it in other words, if you don’t look for it you won’t find it.Historical testing methods required submission to a reference laboratory and in some instances the submission of paired samples.In 2015 point of care testing for leptospirosis was introduced in the United States and as of now two testing options are available.Vaccination can interfere with point of care testing and when these patient side tests are used it is important to have the dog’s vaccination history available and an understanding of the potential limitations of the test in differentiating a vaccine response from natural infection.7,8The window of post-vaccination interference has been demonstrated to be much shorter when an IgM based test is used.8

Consider the Risks

Both patient lifestyle and environment are critical considerations, especially when making vaccination decisions.The large breed male hunting/sporting dogs once thought to have the highest risk of infection have some company.Leptospirosis is often diagnosed in suburban and urban dogs, even those that are strictly indoor or leash walked exclusively.Anywhere that could be contaminated with urine from rodents or wildlife is a potential source of infection.Fresh water is a possible source as well and it is important to look beyond lakes and streams and recognize that even pooled water on impervious surfaces, commonly known as puddles, can pose a risk as can flooding.Preventing exposure to such areas is difficult if not impossible to do.With respect to the environment, it’s important to note that history doesn’t always repeat itself.For this reason historical prevalence data should not be the sole consideration.A 2017 publication evaluating environmental and socioeconomic risk factors found that deciduous forest cover and low density developed land were potential risk factors.9

All of the above are reasons why leptospirosis should be included as a differential diagnosis for many dogs and vaccination should be considered for all dogs, recommended for most dogs and included as a core vaccine antigen in many areas.